hi Vincent007
1.debug build
2.Yes,The refresh speed is very quick, not a bit dull, but I don't like with append, because append broken the original data format, especially the received data is Chinese。The original format:
你好！
我很认真，但是很失望。一直再等待。
If you use the append may become the following format：
你好！
我很认真，
但是很失望。
一直再等待。
3.I once did a test, use a non UI thread interval 1ms to control sending data, display data using insert, long time after will refresh is not over, the main UI can't move。
4.I think QT is text controls render caused by slow。

hi Vincent007
1.I have done a test release version using append fast.no problem。

but I don’t like to use append, because append broken the original data format, especially the received data is Chinese。The original format:
你好！
我很认真，但是很失望。一直再等待。
If you use the append may become the following format：
你好！
我很认真，
但是很失望。
一直再等待。
Thank you for your reply

The slow operation took 10685984 nanoseconds
The slow operation took 10668154 nanoseconds
The slow operation took 10564419 nanoseconds
The slow operation took 10569686 nanoseconds
The slow operation took 10243486 nanoseconds
The slow operation took 10473245 nanoseconds
The slow operation took 10746766 nanoseconds
The slow operation took 10772700 nanoseconds
The slow operation took 10583059 nanoseconds
The slow operation took 11221681 nanoseconds
The slow operation took 10795798 nanoseconds
The slow operation took 16827051 nanoseconds

The slow operation took 222369451 nanoseconds
The slow operation took 205003460 nanoseconds
The slow operation took 222164411 nanoseconds
The slow operation took 204823949 nanoseconds
The slow operation took 209414655 nanoseconds
The slow operation took 186572559 nanoseconds
The slow operation took 209589304 nanoseconds
The slow operation took 214433676 nanoseconds
The slow operation took 219041401 nanoseconds
说明qt的窗口刷新确实有问题，请指教谢谢。